The proposed investigation is the follow-up (and final stage of a project aimed at filling in some key knowledge gaps concerning the properties of under-developed intellectual processes under specified stimulus conditions in a population of educationally retarded, disadvantaged Israeli youth. The intention has been both to describe the static organization of intellect and to analyze its dynamic interaction with certain mediating devices (referred to as "instrumental enrichment") under several controlled environmental conditions. To date, research efforts have involved: 1) A descriptive analysis of the cognitive functioning of the target group; 2) A determination of the extent of modifiability of cognitive functioning of this group; 3) and an assessment of the relative impact of selected highly controlled stimuli and of certain environmental settings upon the redevelopment of cognitive functions. The follow-up stage involves 1) an assessment of the target group's cognitive functioning in educational, occupational, and military settings for two years following termination of the experimental intervention period; 2) a systematic analysis of familial, environmental, personality, and intellective factors associated with success and failure in post-intervention cognitive performance and social adaptation; 3) an assessment of the cognitive functioning of a random sub-population of the target group after supplementing the experimental intervention period with an additional two years of instrumental enrichment and; 4) an assessment of the effects of instrumental enrichment on the cognitive functioning of retarded early adolescents representing etiologies different from the initial target group. Finally an attempt will be made to relate this study's findings about systematic redevelopment of cognitive functions to the reformulation of educational goals and their pursuit through curricular, interventions.